This tool concatenate two FASTA files in a tail-head manner. First you must upload your FASTA files using Upload File tool in the Get Data subsection. After the uploading process is completed, you will select the FASTA files here in this Concatenate tool by selecting them as FASTA file 1 and FASTA file 2. Click on Execute to start the job. Your concatenated FASTA file will be generated and it will be available to download once you click on the name of the job in the History menu at the right side of the screen in the Download option (small disk icon).